1.Technical Field of the Invention
2.Related Art
In vehicles with engines (i.e., internal combustion engines), a starter is usually used to start the engines. Though a variety of types of starters are known, one type of such starters is provided with a magnet field type of electric motor having an armature and a field coil, a solenoid, and a switch. The solenoid is used to push, using a shift lever, a pinion gear toward a ring gear attached to an on-vehicle engine. The switch turns on/off a main contact arranged in an electric circuit for driving the motor (known as a motor circuit), in which the motor circuit drives the motor by supplying current from a battery to the motor. This kind of starter is disclosed by Japanese Utility Model No 56-42437.
In this configuration, the solenoid and the switch can be operated independently of each other. For example, only the solenoid is driven first to make the pinion gear to engage with the ring gear, and then the switch is operated to close the main contact so that the current is supplied to the motor. By this sequential operation technique, the motor can be driven to start the engine after completion of engagement between the pinion gear and the ring gear.
In the foregoing starter, the solenoid to push the pinion gear has an electromagnetic coil composed of two coils. These two coils are an attraction coil to generate a magnetic force necessary for attracting the plunger and a retention coil to generate a magnetic force necessary for retaining the attracted plunger. It is usually required that both one end of the attraction coil and one end of the retention coil be electrically connected to a connector or other electric terminal members. Further, the other end of the attraction coil is electrically connected to fixed contacts of the main contact, so that when the main contact in the motor circuit is closed by the electric switch, the attraction coil is short-circuited via the main contact, that is, no current passes through the attraction coil.
Furthermore, in the starter disclosed above, the electromagnetic coil of the solenoid and the filed coil of the motor are electrically connected by a wiring member with each other. This electrical connection intends to allow current to flow to the field coil via the electromagnetic coil without closing the main contact whenever the pinion gear is brought into contact with the ring gear axially pushed by the solenoid. In other words, the current flows through the field coil via the electromagnetic coil. This current flow makes the armature of the motor rotates slightly, thus making the pinion gear rotates slightly in response to transmission of the slight rotation of the motor armature to the pinion gear, thus allowing the pinion gear and the ring gear meshes on each other.
However, in the structure disclosed by the foregoing starter, the electric circuitry is complicated, resulting in a larger number of parts necessary for the electric circuit. In addition, various working steps are required for manufacturing the starter. Such working steps include a step in which one end of the attraction coil and one end of the retention coil are electrically connected to, for example, a connector, a step in which the other end of the attraction coil is electrically connected to the fixed contacts of the main contact, and a step in which the electromagnetic coil of the solenoid to push the pinion gear and the field coil of the motor are mutually electrically connected by a conductive wire. These many working steps result in an increase in the manufacturing costs of the starter.
Additionally, the foregoing disclosed starter has a difficulty that permanent magnets cannot be used as the magnetic field system of the motor. That is, this starter is obliged to employ a field coil as its magnetic field system. The disclosed technique by the foregoing publication cannot be applied to permanent magnet field type of motors which use permanent magnets in their magnetic field system.